Message-ID: <20130703143452.GA2686@sivokote.iziade.m$>
Date: Wed, 3 Jul 2013 17:34:52 +0300
From: Georgi Guninski <guninski@...inski.com>
To: Valdis.Kletnieks@...edu
Cc: "full-disclosure@...ts.grok.org.uk" <full-disclosure@...ts.grok.org.uk>
Subject: Re: tor vulnerabilities?

Valdis,

I see no reason to trust tor.

How do you disprove that at least (say) 42% of the tor network
is malicious, trying to deanonymize everyone and logging
everything?

Or maybe some obscure feature deanonymize in O(1) :)


On Sat, Jun 29, 2013 at 08:05:17PM -0400, Valdis.Kletnieks@...edu wrote:
> On Fri, 28 Jun 2013 23:37:45 -0400, Neel Rowhoiser said:
> > I just stumbled across this and despite its sort of half-assed write up, I
> > think its possibly an advisory? If I am understanding it correctly, they're
> > saying that you can use a directory authority that hands out invalid/wrong RSA
> > keys for other relays, you can cause decryption to fail and thus introduce path
> > bias to nodes of the directory authorities choosing by selectively handing out
> > valid RSA keys?
> 
> Oh, it's *that* attack again (as far as I can tell).  Some French guys did a
> proof-of-concept a few years ago that you could do this sort of thing if you
> subverted a sufficient number of nodes.  But keep reading.
> 
> > If the bit towards the end about guard nodes is correct, it would seem to
> > indicate that they can use the semantics for detecting when a guard is causing
> > too many extend relay cells to fail to cause valid guards to be marked invalid,
> > and their rogue guards to succeed essentially using tor's semantics against
> > them and causing the odds that you-re ingress point to the tor network is rogue
> > to approach 1.
> 
> The problem is that you have to subvert a large number of relays to
> do it, in a way that doesn't get noticed..
> 
> > Why aren't the tor relay keys signed? And what other myriad of documents do
> 
> And who would sign said relay keys?  They're all essentially self-signed
> already, so what you're looking for is a PKI.  And the whole point of the tor
> system is that nobody involved trusts a central authority.  If you've got a
> good idea on how to do it, feel free to comment.
> 
> > directory authorities serve that also don't have integrity controls? This sort
> > of makes me question the tor projects ability to deliver on any of the promises
> > they make, as it would seem that a person needs like 3 or 4 rogue nodes before
> > they could start de-anonymizing users, and the more of them they introduced the
> > more of the network they could capture?
> 
> Actually, it's more like 3 or 4 *hundred* nodes.  As I write this, there
> are 3,903 relays connected, 1,218 guard nodes, and 2,396 directory mirrors.
> 
> http://torstatus.blutmagie.de/
> 
> Even if you control 400 of those routers, the odds that any connection will
> only traverse your nodes is only 0.1% or so.  If you have "3 or 4', it's
> literally a one-in-a-billion shot.  Assuming a million tor tunnels form a
> day, you'd catch one circuit every 3 years or so.  And no guarantee that
> the circuit you caught carried anything you would find useful.
> 
> I suppose you could bring up 4,000 tor nodes of your own, to increase your odds
> of end-to-end control on a circuit all the way to 12% or so. However, that's
> very much a one trick pony, and probably wouldn't work simply because people
> would notice the sudden growth before you got enough nodes connected to do much
> damage.
> 
> And using rogue directory servers to improve your odds doesn't help either.
> Currently, there's a whole whopping 5 'bad exit' routers.  You can improve
> your chances by corrupting stuff so half the exits are bad - but again, that
> will get noticed when a single-digit number hits three digits.  And you need
> to get it up to 4 digits before you have decent odds.
> 
> And yes, the Tor designers are totally aware that this "vulnerability"
> exists - the problem is that all proposed solutions so far are even
> worse (for instance, requiring signed relay keys).
> 



> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.grok.org.uk/full-disclosure-charter.html
> Hosted and sponsored by Secunia - http://secunia.com/

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

Powered by blists - more mailing lists